The present invention relates generally to rotary machining tools, and more specifically to a rotary turning apparatus used for machining superalloys and other difficult-to-machine metals and alloys at high speeds.
With the need to increase machining speed for improving productivity and reducing procurement costs, tool wear becomes a critical factor limiting productivity. This is especially important when machining materials for aerospace application such as titanium alloys, nickel base superalloys and steel alloys used in gun barrels, e.g., AISI 4340. The majority of tool materials react with the specified work materials; and as speed is increased (in the conventional speed range), tool-chip interface temperatures increase rapidly and this additionally aggravates the chemical interactions between the tool and the chip, leading to rapid tool wear. In order to achieve reasonable tool life between regrinds or insert changes, especially at high cutting speeds, it is necessary to come up with an innovative way of prolonging tool life. Development of new tool materials that can resist wear when machining these materials at high speed is one obvious approach, and tool manufacturers are continuously working towards this goal. However, since no such tool material is currently available, innovative methods have to be devised that will permit the use of conventional tool materials and also provide a decrease in the wear rate or an increase in the tool life. Some of the methods by which this objective can be accomplished are:
effective cooling of the tool by reducing the rate of increase of the chip-tool interface temperature;
providing a continuous (or infinite) cutting edge; an
effective contamination of the chip tool interface to reduce chemical interactions.
Rotary cutting tool machining appears to be one promising method for achieving the objectives. It is basically a cutting process in which a fresh portion of the cutting edge is fed continuously to the cutting zone in addition to normal feed and depth of engagement (or cut).
A rotary tool is a cutting tool with a circular cutting edge that rotates about its own axis, either self propelled by the cutting process or driven externally at the desired speed. The cutter is attached to a spindle that rotates between suitable bearings. As cutting progresses, new portions of the cutting edge are continuously brought in contact with the workpiece at the cutting zone. Representative examples of rotary tool systems are disclosed in the following U.S. Patents, the disclosure of which are incorporated herein by reference:
U.S. Pat. No. 2,551,167 issued to Rolland; PA0 U.S. Pat. No. 2,651,223 issued to Hahn; PA0 U.S. Pat. No. 2,663,977 issued to Gerard et al. PA0 U.S. Pat. No. 3,578,232 issued to Loyd et al. PA0 U.S. Pat. No. 3,732,757 issued to Cottin; and PA0 U.S. Pat. No. 4,223,580 issued to Sidorenko et al.
The patent to Rolland has been selected to illustrate a rotary cutting tool of the general class discussed in the present. The reference Hahn has been selected to show that use of a single spherical ball to receive axial thrust loads in a cutter is well known in the art. The references Gerald et al. and Loyd et al. have been included for their showing of the use of high pressure hydraulic fluid in connection with high speed rotating spindles but neither singly nor jointly do they suggest the present invention's use of high pressure fluid. The reference Cottin is of interest in its showing of use of hydraulic fluid in high speed rotary machine tool. The patent of Sidorenko is of interest and has been included as possible background information in the rotary cutting art.
While the above-cited references are instructive, rotary machining systems have some inherent problems. For example, the need to increase machining speeds to improve productivity and increasing use of superalloys for aerospace applications are imposing severe restrictions on the potential life of a cutting tool. Generally, the cost of an insert is only a small fraction (often times negligible) of the total cost. Considerable non-productive time, such as the insert changing time and/or tool regrinding time, is involved.
In view of the foregoing discussion, it is apparent that there currently remains the need for an improved rotary machining system which will increase the life of the tool between insert changes. The present invention is intended to satisfy that need.